Radiant or electromagnetic energy emitters and distributors find a wide range of applications in modern society. Visible illumination systems, for example, illuminate areas and surfaces to enable use by personnel in locations or situations in which natural ambient lighting might be insufficient. Infrared illumination is a critical component of many night-vision technologies. Other lighting devices provide guidance or warnings, for example to enable pilots to locate the edges of runways or taxiways, to illuminate emergency exit paths, to visibly indicate an emergency condition, etc. Different applications of radiant energy illumination systems require different performance characteristics.
Simple radiation sources, such as light emitting diodes (LEDs) or light bulbs with reflectors and/or lenses typically provide a high intensity radiation in regions close to the axis of the field of view/illumination, but the intensity drops off quickly at off-axis angles approaching the horizon. On a system illuminated by such a source, the intensity is not uniform. To provide a desired illumination at edges of a design footprint, the source often will emit substantially higher amounts of radiation than necessary along the axis.
Prior attempts to provide desired intensity distributions have involved complex arrangements of sources, lenses and reflectors. These complex arrangements tend to be relatively expensive and sensitive to problems of misalignment, which limits ruggedness and durability.
U.S. Pat. No. 5,733,028 issued Mar. 31, 1998 to Ramer et al. discloses a number of embodiments of illumination systems that utilize constructive occlusion. With this technology, a mask occludes an active optical surface, typically a Lambertian surface formed by the aperture of a diffusely reflective cavity, in order to distribute radiant energy with a tailored intensity distribution. Adjustment of the parameters of the constructive occlusion system enables the system designer to tailor the system performance to a wide range of applications. Constructive occlusion typically emphasizes distribution based on multiple diffuse reflections within a mask and cavity system. Careful selection of the system parameters, such as relative sizes of the mask and aperture and the distance between the mask and aperture, can adapt the constructive occlusion system to meet the requirements of many diverse illumination applications.
U.S. Pat. No. 6,334,700 issued Jan. 1, 2002 to Ramer et al. discloses constructive occlusion systems, which also provide a direct illumination component. The constructive occlusion provides a desired intensity illumination over one field, and direct radiation from the source, through a gap, opening or lens or the like, illuminates an additional field. The fields may overlap, or they may be separated. In several of the examples disclosed in this patent, the direct illumination provides a higher intensity illumination than the tailored intensity illumination provided by the constructive occlusion.
U.S. Pat. No. 6,286,979 issued Sep. 11, 2001 to Ramer et al. discloses constructive occlusion systems, but this patent teaches addition of a port from the constructive occlusion cavity and a reflective fan as a deflector to distribute additional energy emerging through the port into a desired region to be illuminated. With respect to the port and fan, the cavity and mask of the constructive occlusion system serve as the optical integrating cavity. The constructive occlusion emissions provide a tailored intensity distribution for radiant energy illuminating a first region. The integrating cavity, port and deflector (fan) distribute another portion of the electromagnetic energy over a second field of intended illumination. The first and second regions illuminated may overlap slightly, or one may include the other, but preferably most of the two regions are separate. In some cases, the system configuration creates a dead zone between the two regions.
The techniques disclosed in the identified patents allow a system designer to distribute light or other radiant energy in a wide range of different patterns, for a myriad of diverse illumination applications. However, even these techniques do not satisfy the requirements of all desired applications.
Consider indirect illumination as an example. Indirect illumination involves radiating energy against a face structure, which in turn reflects the energy into a region of actual interest. In lighting a room, for example, an indirect lighting type fixture might directly radiate or illuminate a wall or ceiling. Actual illumination of a work area in the room would then use light reflected (indirect illumination) from the wall or ceiling. To provide desired intensity and a pleasing appearance of the lighting fixture, however, it would be desirable if the fixture provided at least some light emission into the room without reflection from the face structure, although the main illumination may still be that provided indirectly through illumination against the ceiling or wall.